make sure you use SATA when you buy the HD..
also, check warranties, seagate for example has only like 1 year..
the waranty won't really matter if the drive is going to last,
and last and last and last and last and last ..........
also, the warranty really depends on where you get the parts; different places, different warranty.
You dont need a dvd drive if you already have a combo drive, might lower the price a bit if your on a budget
he's getting a DVD+/- burner and a CDR/RW/DVD drive
the DVD burners are not incredibly fast yet, so the CDR/RW/DVD being 52x24x52x16 will get faster speeds for normal use - including on DVD disks - so there will be no/less latency, you'd only use the DVD burner for..... well, burning DVD's
also, you might want to watch what brands you get; picking a "bad" brand drive can leave you with just a dead/faulty box (the drive, not the PC)
Sony, Pioneer or LG would be my choices
OS: Mandrake, Redhat, or Whitebox Enterprise Linux, or Windows 2000, XP or 2003